Ethylene propylene (EPM) rubbers are synthetic copolymers made by the stereospecific copolymerization of ethylene and propylene. When combined with a third monomer such as diene the resultant ethylene-propylene-diene (EPDM) is a particularly fine synthetic rubber and is felt to be particularly useful in a membrane-type filter plate.
Such a filter plate has a central rigid panel with two opposite and planar faces and formed with a T-shaped passage opening at its edge and at a central location in each face. Overlying each face is an elastic sheet formed with a thick annular rim bounding a ribbed central region. The elastic sheets are joined at the rims to the respective faces of the central panel. In use a plurality of such filter plates is stacked with two mesh filter media pinched between confronting rims of the elastic sheets. Connections are provided to feed an unfiltered suspension to the chamber between two adjacent meshes and to draw off filtrate from between each mesh and the respective ribbed sheet. Periodically the apparatus is pumped out as air or another fluid under pressure is introduced between each elastic sheet and the respective panel face so as to bubble out this sheet and compress the filter cake between the two meshes, making it possible to reverse-flush this filter cake out.
For best operation and ease of assembly the two elastic sheets should be very solidly bonded at their rims to the respective faces of the rigid center panel. Although vulcanizing EPDM to a metal is known from the bumper or shock-absorber art, it is normally not considered possible to solidly bond the EPDM to a thermoplastic synthetic-resin panel of the type ideally used in such filters.